Hydrogels have been recently attracting attention from the viewpoint that hydrogels are soft materials having high biocompatibility because of containing water as the main component and having a low environmental load.
Water-soluble polymers such as polyacrylamide, polyacrylic acid, and polyvinyl alcohol are widely used as components of hydrogels. Among them, organic/inorganic composite hydrogels containing a polyacrylamide-based or cross-linked polyethylene glycol-based water-soluble polymer and a layered clay mineral allows successfully improving the strength of hydrogels, which has markedly expanded the range of their use (Patent Document 1 and Patent Document 2). Versatile organic/inorganic composite hydrogels have been recently disclosed that can be produced simply by mixing a polyelectrolyte, clay particles, and a dispersant (Non-Patent Document 1 and Non-Patent Document 2).
The use of hydrogels extend to an extremely wide range including medical use, quasi-drugs, cosmetics, daily necessities, food, electronic materials, agricultural materials, building materials, toys, sanitary materials, and biological bases, and hydrogels are used after being processed and formed in accordance with the respective uses. To process a self-supporting hydrogel, in addition to the production of a gel in a mold and extrusion molding, forming can be performed by removing unnecessary parts through cutting, punching, or the like. However, these pieces of work are extremely difficult or complicated for the production of hydrogels that require complicated shapes. In view of working efficiency, production by assembling fine components by bonding is simple. Bonding is extremely convenient also for the repair of broken parts such as cracks and ruptures in already completed hydrogel molded products. Thus, a method for bonding together hydrogels is being demanded.
As a method for bonding together hydrogels, a method is known in which surfaces to be bonded together are impregnated with a reactive monomer, the surfaces to be bonded together are brought into close contact and then subjected to a polymerization reaction, thereby a polymer network is formed (Non-Patent Document 3). Another method is known in which opposite ionic gels such as polyanions and polycations are bonded through electrostatic interaction (Non-Patent Document 4). Still another method is known in which, bonding of the same ionic gels is performed through opposite ionic fine particles (Patent Document 3). Recently disclosed are hydrogels that have self-repairability and allow bonding together even fresh surfaces that have just being cut (Patent Document 4 and Non-Patent Document 5).